1. Field of the Invention
The present invention relates to an optical fiber bundle, a light source device using the optical fiber bundle, and a method for manufacturing the light source device, and particularly relates to control of an output light intensity distribution of the optical fiber bundle in the light source device.
2. Description of the Related Art
An optical fiber bundle has several to several thousands of a bundled optical fiber. The bundle optical fiber are bonded and polished in terminal portions of the optical fiber bundle. The optical fiber bundle is used widely for lighting or energy transfer. As shown in FIG. 11, both end portions 120 and 130 of a tube 10 of a optical fiber bundle are typically fixed with sleeve-like metal fittings or the like, but flexibility is secured in the intermediate portion of the optical fiber bundle. Accordingly, the light input area or output area of the optical fiber bundle can be increased while the degree of spatial freedom thereof is secured. Accordingly, when the output area is made extremely small and an optical fiber light source is placed in a desired place, the optical fiber bundle can be installed in any place.
Thus, attempts in various fields are made to apply light source devices using optical fiber bundles to light sources for exposure in light steppers or light sources for curing photo-setting resin for use in bonding of optical components or the like.
In such circumstances, there is a request to make the output light intensity distribution uniform. In an optical fiber bundle shaped into a ring on its output side, there is another request to form the output light intensity distribution uniform concentrically and circumferentially.
In addition, when a light source device is used as a light source for exposure in a stepper, it is necessary to change the wavelength of exposure light in accordance with a resist or to adjust the irradiation energy. Thus, a different light source device is required whenever the occasion demands.
Further, a stepper needs a step of aligning a mask with a wafer prior to exposure, that is, a mask alignment step. A light source having a different wavelength from the sensible wavelength of a resist is required in the mask alignment step. Thus, two different light sources are required. Alternatively, there is indeed a method in which the light intensity of a light source for exposure is reduced on a large scale at the time of alignment so that the light source is used as a light source for alignment. However, there is a problem that it is inevitable to expose the resist to light at the time of alignment.
Moreover, it is desired to regulate an area to be irradiated at the time of alignment because it is not necessary to irradiate the wafer surface as a whole but it will go well if only an alignment mark provided in a dummy area such as a wafer circumferential edge portion is irradiated. However, existing light source devices cannot perform such area definition.
In addition, it is necessary to reduce the light intensity in the area corresponding to the circumferential edge portion. It is, however, difficult to reduce the light intensity only in the circumferential portion. When exposure is performed with a regular intensity distribution, overexposure occurs in the circumferential edge portion, resulting in fogging. Thus, there is a problem that a precise resist pattern cannot be obtained.
It is therefore necessary to allow latitude to the irradiation light intensity distribution. In a typical method, however, uniform irradiation with light on the wafer is fundamental, and it is difficult to change the intensity or change the irradiation wavelength for each area.
Furthermore, in recent years, with the development of digital cameras and the like, optical components are made finer and finer. When such optical components are mounted, there is an increasing request to make alignment and fixation more accurate. When optical components are fixed to each other by use of photo-setting resin, it may be desired to perform two-stage curing treatment using different kinds of resin. In such a case, two separate light sources having different emission wavelengths are required as light sources for the treatment. It is therefore difficult to put such a treatment to practical use.
For the request to make the light intensity uniform, in the related art, there is adopted a method in which optical fibers are randomized on the output side of the optical fiber bundle so that the light intensity distribution is adjusted. Optical fibers having a high light intensity are mixed with fibers having a low light intensity appropriately uniformly so that a desired uniform output light intensity distribution can be obtained.
In such a method, the optical fibers are randomized in the optical fiber bundle, and then the output light intensity of the optical fiber bundle is confirmed. If the output light intensity is not uniform as a result of the confirmation, the optical fibers are randomized so that the output light intensity is uniform. Therefore, the yield of the optical fiber bundle and the efficiency of manufacturing are limited by this randomized method.
In addition, an area where the output light is irradiated from the optical fiber bundle cannot be defined or changed in this method.
Further, when the output light intensity is precisely control by using the optical fiber bundle, illuminance near an output terminal of the optical fiber bundle has to be measured by an illumination sensor 600 and fed back to a light source as shown in FIG. 12. However, this results in a problem that the device becomes large in size. In addition, an optical system 200 also becomes a major factor in obstruction to the miniaturization of the device.
Furthermore, even if the light intensity distribution can be controlled with a large-sized device, the wavelength cannot be adjusted by use of the optical fiber bundle in the same light source device.
It is therefore necessary to provide a light source for alignment and a light source for exposure separately.